The present invention relates to a rotating contactor for the biological treatment of waste water.
For the biological treatment of waste water, it is common to use rotating contactors or rotors which are partially submerged in the waste water and adapted to slowly rotate to expose the waste water to the atmosphere or air, whereby organic substances in the waste water are biologically oxidized or treated by the action of the aerobic micro-organisms. A typical rotating contactor is disclosed in U.S. Pat. No. 4,115,268. The contactor comprises an elongate plastic sheet spirally wound in multiple turns on a rotatable shaft in a superimposed relation to each other to form a convolute. The plastic sheet is provided with cup-shaped irregularities to define peripheral flow channels between the turns in the convolute. It is also known to prepare a rotating contactor by spirally winding two elongate plastic sheets at least one of which has embossed patterns to provide flow channels between the sheets. Various structures have been proposed from such elongate plastic sheets.
Such elongate sheets are required to have adequate flexibility in the longitudinal direction so that they can be wound readily on the rotating shaft. At the same time they are required to have sufficient rigidity in the axial or transverse direction. When they are spirally wound on the shaft, they must provide a sufficient number of flow channels which are continuous in both the circumferential and axial directions and yet the spirally wound structure must have adequate radial compressive strength to bear the weight of the biological slime deposited on the sheets and the weight of the sheets themselves. Further, the plastic sheets are required to be readily wound in a simple and efficient means. For instance, there used to be a problem that two different kinds of elongate sheets are likely to be displaced in the transverse direction at the time of winding the sheets on the shaft. Furthermore, it is desired that they can be prepared at a low production cost. None of the conventional contactors adequately satisfy these various requirements.